1. Field of the Invention
The present invention relates generally to electrical devices. Specifically, the present invention relates to a method and apparatus for saving power during punctured transmission in a mobile communication system.
2. Brief Description of the Related Art
The three major types of multiple access networks are frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). In a CDMA system, various users share the same frequency and the same time slot. The users are distinguished (channelized) from each other by assigned code sequences, such as orthogonal codes or pseudorandom noise (PN) codes. Each receiver in a CDMA system separates the transmitted signals from a base station by using a correlator that accepts only signal energy designated to a particular user. Undesired signals constitute noise. A receiver in a CDMA system must filter out these undesired signals.
By transmitting at the same time and sharing the same frequency, the users constitute mutual interference to each other. A CDMA transmitter of one user may substantially reduce the interference generated by the transmitter by reducing the transmission rate when the user""s voice activity is low. When the transmission rate is reduced, there are intermittent bursts (periods or groups) when no voice data is transmitted.
An important factor in designing new mobile communication handsets is saving power, which directly affects the battery life and the xe2x80x98talk timexe2x80x99 of the handset. As smaller form factors limit the size and type of components used, including battery cells, power savings is becoming more critical in current wireless communication devices.
IS-95 is a digital standard or protocol for CDMA cellular system operation. IS-98 is a test standard derived from the IS-95 standard for CDMA mobile stations. IS-95 CDMA mobile communication systems enhance the capacity of the network and save power in the handset by taking advantage of the nature of human speech. In CDMA systems, voice or speech activity is not always present during a two-way conversation. Statistically, in a two-way conversation, the voice activity from one side (voice activity factor) in a full duplex, CDMA system commonly only comprises 40% or less of the total speech time. For the remainder of the speech time, there is no voice activity from one side and no information being transmitted from that side.
In general, a mobile communication handset commonly comprises a radio frequency (RF) frontend portion, a mixed signal portion or interface, a baseband device, a microphone and a speaker. In existing CDMA handsets, a voice coder (vocoder) reduces the rate of voice data transmission when there are pauses in a user""s speech. The reduction in the transmission rate creates intermittent bursts in the baseband device when no voice data is transmitted.
To save power on a mobile handset, it is desirable to momentarily and selectively power OFF certain portions of the handset during an intermittent burst in the baseband device when no voice data is transmitted. In existing IS-95 CDMA systems, the handset powers OFF certain components of the RF frontend portion, such as a power amplifier (PA) and other drivers, during an intermittent burst in the baseband device when no voice data is transmitted. The handset powers the components back ON when there is a burst with voice data to be transmitted. But the remainder of the RF frontend portion, such as a mixer and variable gain amplifiers (VGAs), and the mixed signal portion are always ON in existing systems.
The present invention uses a signal or command to selectively power (gate) OFF and ON certain components of the mixed signal portion during intermittent bursts in the baseband device with no transmitted voice data. In one embodiment, these components include a digital-to-analog converter (DAC), one or more switched capacitor filters, and one or more continuous time smoothing filters. In one embodiment, a burst in the baseband device is 1.25 milliseconds long in a 20 msec frame. In one embodiment, the signal is based on a command from a modem inside the baseband device. In another embodiment, the signal is generated by a voice coder (vocoder) inside the baseband device. In another embodiment, the signal is generated by a vocoder outside the baseband device. In one embodiment, the signal is generated by a processor inside the baseband device.
The present invention saves significant amounts of power and thereby increases talk time. Because the voice activity factor is typically 0.40 or 40% or less, the present invention can save approximately 60% of the power consumed by certain components in the mixed signal portion.